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(CNN) -- More research is needed to determine whether potentially dangerous life forms exist on Mars before a manned mission to the Earth's nearest planetary neighbor can go ahead, a NASA advisory panel has warned.

The Mars Exploration Program Analysis Group (MEPAG), which was established to assist in the scientific planning of Martian exploration, said that astronauts could inadvertently carry microbial life back to Earth.

"The most significant risk identified is that associated with the possibility of transporting a replicating life form to Earth, where it is found to have a negative effect on some aspect of the Earth's ecosystem," MEPAG said in a report published this month.

"Most scientists would agree that the probability of a negative consequence is very low, but the consequences could potentially be very large."

In 2004 U.S. President George W. Bush announced plans to send astronauts back to the moon by 2015 as a stepping stone for further manned trips to Mars -- perhaps by 2030.

But MEPAG recommended that a robotic mission to return Martian soil and air samples to Earth for analysis was required before a manned mission could be approved.

Currently no such mission is planned and the New Scientist magazine reported that designing and building a facility to analyze and store the samples safely would take an estimated 10 years.

"If life is found in any sample it must be assumed hazardous until proven otherwise," the report warned. "Hazard determination is complex, and involves the understanding of possible hazard to Earth's biosphere, crew health, and potential spacecraft and habitat equipment and materials.

"These determinations may require extensive experiments, which would be carried out in laboratories on Earth."

MEPAG also said that further research was needed into whether the dust on the Martian surface posed a toxic risk to humans or would interfere with the performance of machinery.

Data collected by NASA's Spirit and Opportunity rovers, which have been studying geology on opposite sides of Mars for more than 15 months, may help scientists address those issues.

Studies of Mars' upper atmosphere and determining potential sources of water -- which could be broken down into breathable oxygen and hydrogen fuel -- were also considered priorities.

NASA will send a stationary lander, named Phoenix, to study Mars' icy northern plains in 2007. It will look for potential habitats for water ice and for possible indicators of current or past life.